The family of poly(3,4-alkylenedioxypyrroles) are known to be useful polymers for the fabrication of a wide variety of products. Useful monomers for this family of polymers include N-alkylated 3,4-alkylenedioxypyrroles. Such products include electrochromic windows, mirrors and displays, electronic paper, anti-stat conductors, transparent conductors, field effect transistors, supercapacitors, batteries, photovoltaic devices, and other electronic components due to their elevated band gaps, low oxidation potentials, biological activity, and flexibility toward functionalization. Present synthetic routes to the N-alkylated 3,4-alkylenedioxypyrrole monomers are expensive as the synthetic pathways are difficult and inefficient and their isolation typically requires chromatography which significantly raises the cost and significantly limits the product throughput provided by the process.
To illustrate the present state of the art, a prior art synthetic pathway is described below for the synthesis of a soluble N-alkylated 3,4-alkylenedioxypyrrole, N-(octyl)-3,4-propylenedioxypyrrole, as disclosed by Sönmez, G.; Schwendeman, I.; Schottland, P.; Zong, K.; Reynolds, J. R. Macromolecules 2003, 36, 639-647. FIG. 1 illustrates this method for N-(2-ethylhexyl)-3,4-propylenedioxypyrrole. The synthesis begins with the reaction of benzylamine with methyl bromoacetate to yield a diester which undergoes the heterocyclic ring-formation via a Hinsberg condensation with diethyloxylate to yield a dihydroxypyrrole. The propylene bridge is then formed via Williamson etherification of the dihydroxypyrrole with 1,3-dibromopropane to yield an ester substituted 3,4-propylenedioxypyrrole. The next step involves the catalytic debenzylation of the ester substituted 3,4-propylenedioxypyrrole in glacial acetic acid with a palladium catalyst over a period of five days. The resulting diester hydropyrrole, is then saponified to yield a diacid, which is then converted to propylenedioxypyrrole via decarboxylation in triethanolamine. Propylenedioxypyrrole is then functionalized to yield a derivative, such as N-(2-ethylhexyl)propylenedioxypyrrole.
This pathway is undesirable from a commercial standpoint for several reasons. This synthesis of a soluble propylenedioxypyrrole requires seven transformations, two of which require a protected nitrogen using an atom inefficient benzyl group and its subsequent deprotection. In particular, the fourth step that yields an ester substituted 3,4-propylenedioxypyrrole is undesirable from a commercial standpoint due to its long reaction time, expensive reagents, and the use of a toxic palladium catalyst.
There remains a need to develop a method of preparing N-substituted 3,4-alkylenedioxypyrroles in a manner that is efficient and cost effective with less toxic reagents and catalysts. There also is a need for flexible intermediates such that N-substituted 3,4-alkylenedioxypyrroles with a wide variety of substituents can be formed such that the structure of these monomers and ultimately the polymers from them can be modified to develop properties needed for existing and future uses of the conjugated poly(3,4-alkylenedioxypyrrole)s.